0xDEADBEEF

So, I screwed up the DES example somewhere I think.  I’m fairly sure, anyway.  Yeah.

Somewhere in:

First 8 iterations of DES Example

I made a mistake.  I’m fairly sure the setup was correct:

Initial DES Setup Steps

And the first few iterations:

DES Iteration 1

DES Iteration 2

DES Iteration 3

You can see where I botched R’(2) by shifting the wrong values around.

Then F(3), K(4), R’(4), C(6), K(6), F(5), R(5), R(8), D(9), K(9), F(8), R(9) …

DES Iteration 4

DES Iteration 5

DES Iteration 6-7

DES Iteration 8

Those are the errors I found while I was working.

I’m also fairly sure that at some point I started getting R and L confused, in F most likely, when I’m XOR’ing.  And I just didn’t have the … energy to go through it all to find the issue.  I may work it after thanksgiving, or I may restart it in a more structured manner that will force me o keep track of the C D L R in proper manners.

OTOH, If I ever get this done properly and find a good way of displaying it, this is basically what I started this blog for.  Showing the process, so that it’s easier to grasp, rather than just the mathematics and the sometimes hard-to-follow standards definitions.  Not that I’m looking forward to MD5, RSA or Blowfish, for example

Tags: Demonstration, DES
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So, as I was finishing iteration 9 (yeah, this is taking longer than anticipated, because frankly it’s a bit tedious and requires that I have some decent space on the train) I found myself making an error in structure.  I was XORing R(i-1) with F(i) to get R(i) , and it should be L(i-1) …

Which means I need to go back and review iterations 1-8 and make sure I didn’t make this mistake earlier.  And if I did, I have to restart from that point, because the math will propogate :/

It may be a few more weeks before this gets posted.  And I still need to figure out a good mechanism for displaying it rather than just table after table.  I may look into some kind of graphical table or something  ; I’d like to do some kind of overlaying of grids to the numbers to show, but that might take some fancy flash and I don’t have flash

Tags: Demonstration, DES
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I wanted to let folks know that I’m working on the DES example (nee demonstration).

I’m currently doing it while I’m on the train every day, usually in the evening now that the fall season is starting up and iTunes is having my shows again  But it’s slow, and some days I just feel like reading my book.

Anyway, each iteration takes ~3 half-sheets (I’m folding papers over and using half a sheet to write on, just because it gives me a contained space that’s easy to hold on to for writing). It looks like I can do 1.5-2 iterations a day at this point, but I’m only done with the 3rd iteration, so that may be over or under.  The first iteration took a day, then I finished the next two in one day give or take, but the XORs are starting to get more complex … Hopefully will be done by the end of the month, then I’ll have to work on typing it all in.  I want to get them posted in a row, though, so it’ll be a while before they start posting.

I did change the example some, however, so the old start is no longer relevant.

Tags: Demonstration, DES
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